A Spiro curve is a curve defined entirely by its points, you don’t have to worry about handles. The resulting curve uses the minimum possible curvature to pass through the points. The visual result is that it becomes very easy to build very natural, smooth and nice paths.

The second feature of this screencast is freehand shapes. Basically, before this the pencil tool could only draw lines of constant width, with freehand shapes, you just choose the type of line you want to draw.